1. Field of the Invention
The present invention relates to a material handling vehicle, such as an excavator and, in particular, to an apparatus for stabilizing such a vehicle during manipulation of its material handling implement.
2. Description of the Prior Art
Frequently, a heavy duty material handling mechanism such as a crane or excavator is mounted on an upper structure which is pivotally supported on a lower or truck chassis. The truck chassis is capable of being driven over the road or highway under the control of an operator in a main truck cab provided on the truck chassis. The material handling mechanism is supported on the upper structure which is mounted on the truck chassis by means of a swing bearing through which a center pin extends so as to provide relative movability of the upper structure with respect to the truck chassis. An upper structure operator's cab is provided on the upper structure to move with the material handling mechanism. During operation at a contruction site, an operator in the upper structure operator's cab can control movement of the truck chassis and also of the material handling mechanism.
In the case of a material handling vehicle such as an excavator, a telescoping boom means is preferably vertically pivotally mounted on the upper structure with a material handling implement, such as a bucket, attached to the free end of the boom. The boom means is typically capable of being raised or lowered by means of a hydraulic cylinder connected between the boom support cradle and the upper structure. In addition to the extension and raising of the boom, such booms are also often capable of being tiltable about their axis, or, most preferably, from side to side about a pivot axis remote from the boom axis. Also, as indicated above, the upper structure is preferably horizontally pivotable upon the lower chassis in order that materials may be handled at distances remote from the vehicle and located on virtually any side thereof.
A problem which invariably arises in connection with the handling of articles remote from the vehicle is the stabilization of the vehicle during such handling. It is well known that the instability of the vehicle, if not compensated for, markedly reduces the vehicle's loading capacity at virtually all distances and locations therefrom. Such instability can cause vehicles to fail under remote loadings with potentially catastrophic results.
The principal prior art means for stabilizing material handling vehicles includes the provision of outriggers which extend from the four corners of the vehicle. While the outriggers overcome some of the instability problems, they are fraught with difficulties of their own. For example, the additional times required to extend, set and secure the outriggers reduce the operating time available for the vehicle. Further, the additional engineering, manufacturing, and maintenance times required by the provision of outriggers add considerably to those costs of the vehicle's operation. Also, outriggers add to the weight of the vehicle and may even require the provision of additional axles thereby adding further to vehicle cost. In addition, outriggers are proven to destroy the surface of blacktopped areas when used thereon.
An alternative means for stabilizing material handling vehicles has included the provision of hydraulic cylinders between a non-spring suspended axle of the vehicle and its frame along with means for locking the hydraulic fluid in the chambers of the cylinders. The actuation of such a system was usually manual. Further, even if automatic, such systems have been insufficient to provide effective stabilization of vehicles having spring suspended axles or to be automatically controlled by the mere activation of a remote travel controlling joystick. Moreover, even automatic prior systems use hydraulic fluid controls rather than pneumatically controlled means. Known disadvantages to all hydraulic systems include inaccurate control due to viscosity variations with temperature and the added cost of the additional components of hydraulic systems.
The subject invention is directed toward a means for stabilizing a material handling vehicle which overcomes, among others, the above-discussed problems and which provides an effective, efficient and inexpensive means for stabilizing such vehicles without requiring the use of problem-ridden prior art means such as outriggers.